JS random string generator

jsurandom.js

(function(){
	"use strict";

	var URANDSRC = "/dev/urandom",

	getUrandomInt8 = (function(){
		var fs = require("fs"),
		urandom = fs.openSync(URANDSRC, "r"),
		buf = new Buffer(1);

		return function(){
			fs.readSync(urandom, buf, 0, 1, 0);
			return buf.readUInt8(0);
		};
	})(),

	createCharPool = function(type){
		var i = 0,
		ret = [];

		switch(type){
			case "lower":
				for(i = 48; i <= 57; i += 1){
					ret.push(String.fromCharCode(i));
				}
				for(i = 97; i <= 122; i += 1){
					ret.push(String.fromCharCode(i));
				}
				break;

			case "mixed":
				for(i = 48; i <= 57; i += 1){
					ret.push(String.fromCharCode(i));
				}
				for(i = 65; i <= 90; i += 1){
					ret.push(String.fromCharCode(i));
				}
				for(i = 97; i <= 122; i += 1){
					ret.push(String.fromCharCode(i));
				}
				break;

			case "ascii":
				for(i = 33; i <= 126; i += 1){
					ret.push(String.fromCharCode(i));
				}
				break;

			default:
				break;
		}

		return ret;
	},

	echo = function(str){
		return process.stdout.write(str + "\n");
	},
	exit = process.exit,

	argv = process.argv.slice(1),
	argc = argv.length - 1;

	(function(){
		var charPool = [], userLength = 0,
		ret = [];

		if(argc !== 2){
			echo("Usage: "+ argv[0] +" length {lower|mixed|ascii}");
			exit(1);
		}

		if(isNaN(userLength = parseInt(argv[1], 10))){
			echo("Invalid length \u001b[1m" + argv[1] + "\u001b[0m.");
			exit(1);
		}

		if(argv[2] !== "lower" && argv[2] !== "mixed" && argv[2] !== "ascii"){
			echo("Unknown type \u001b[1m" + argv[2] + "\u001b[0m.");
			exit(1);
		}

		charPool = createCharPool(argv[2]);

		(function(){
			var i = userLength;

			for(i; i > 0; i -= 1){
				ret.push(charPool[Math.floor(getUrandomInt8() * charPool.length / 256)]);
			}
		})();

		echo(ret.join(""));

		return;
	})();
})();